Don't have any idea.....

Last year I spent time in Thailand, and of course my Sprint phone was useless.

The I-phone (I don't like Apple products) is Quad-banded, and has sim cards, but I understand that you are somehow locked to a certain carrier.

Are there Quad-banded, sim-carded phones available that can be used with a carrier of choice (I use Sprint Sero now) and which are usable in Asia by buying a local Sim card?

Or is the system still obscenely monopolistic.

Is there any movement going on towards being able to change service providers simply by changing Sim cards?

I haven't even looked at phones for the past few years and am wondering, and not happy that I have to buy a new phone every time I go to Thailand.

Thanks